In an exhaust passage for an internal combustion engine of a vehicle or the like, in some cases, a burner device is provided upstream of an exhaust gas treatment device (a catalyst or the like), the temperature of exhaust gas is raised through the use of heated gas generated by the burner device, and the exhaust gas treatment device is heated to promote warm-up thereof. Typically, the burner device ignites and burns the fuel added into the exhaust passage, thereby generating heated gas including flames (e.g., see Patent Document 1).
By the way, in the burner device, the obtained combustion performance is enhanced as the concentration of oxygen in exhaust gas supplied to the burner device rises. On the contrary, if an attempt is made to obtain combustion performance of at least a certain level in the burner device, the concentration of oxygen in supplied gas needs to be higher than a minimum required concentration of oxygen. This tendency is remarkable especially when the temperature of supplied gas is low.
On the other hand, in recent years, improvements in fuel economy have been made by holding the engine rotational speed low, and the amount of exhaust gas per unit time tends to fall. Meanwhile, the decrease in friction resulting from a decrease in engine rotational speed is small, and there is also a drag resistance of a torque converter in the case of an automatic transmission car. Therefore, the engine load has been higher than before.
In such circumstances, the concentration of oxygen in exhaust gas or hence the concentration of oxygen in gas supplied to the burner device tends to decrease. It has been difficult to stably ensure combustion performance of at least a certain level especially when the temperature of exhaust gas is low.
It is thus an object of the invention to provide a control apparatus for an internal combustion engine that can stably ensure combustion performance of at least a certain level in a burner device.